“Speckle” is an interference phenomenon that occurs when coherent light (e.g., laser light) is reflected from a rough or multiply scattering sample onto a detection plane. Due to scattering of photons from and within the sample, different photons travel different distances to the detection plane. As a result, the light reflected or backscattered from the sample, if spatially and temporally coherent, interferes at the detection plane, producing a grainy pattern known as “speckle.”
Researchers have used speckle pattern analysis to study dynamic movement of tissue in vivo. For example, speckle has been used to measure vibrations of tissue, V. Tuchin et al., “Speckle interferometry in the measurements of biotissues vibrations,” SPIE, 1647: 125 (1992), and to measure strain in vascular and cortical tissue in response to forced movement of the tissue, Sean J. Kirpatrick et al., “Laser Speckle Microstrain Measurement in Vascular Tissue,” SPIE, 3598: 121-128 (1999); and Sean J. Kirkpatrick and Brent W. Brooks, “Micromechanical Behavior of Cortical Bone as Inferred from Laser Speckle Data,” J. Biomedical Materials Research, 39(3): 373-79 (1998). Researchers have also used speckle to study blood flow and lymph flow. B. Ruth, “Blood Flow Determination by the Laser Speckle Method,” Int'l J. Microcirc: Clinical and Experimental, 9(1): 21-45 (1990); and A. A. Bednov et al., “Investigation of Statistical Properties of Lymph Flow Dynamics Using Speckle-Microscopy,” SPIE, 2981: 181-90 (1997).